Out of the blue my car started running like crap and threw code P0171 - fuel system too lean. The comp is dumping do much fuel to compensate that I've used alnost a 1/4 tank in the last 30 miles and the back end of my car is covered in soot. O2 sensor ruled out. Intake leaks ruled out. No exaust leaks. IAC motor is operating fine. The car surges at idle like its misfiring on a cylinder but there are no misses reporting on any cylinders during test drives. Under throttle I have no loss of power and nothing seems weird until I punch it. Then I can pretty much look like a deisel truck. Any ideas what's going on here? I'm at a loss.
Heavy ass N-body
How do you know the O2 sensor is Ok ? and did you check the map sensor ?
I replaced the 02. How do I go about checking a MAP sesnsor?
Heavy ass N-body
my guess would also be MAP...
figure i'll throw out my recent experience with the MAP sensor... same motor so why not..
My STFT showed -18% when idling so i was running rich but the ecu was leaning it out .... also read a 26% load on the motor at idle, numbers started to even out a bit as i started driving... Same symptoms for the most part, 16mpg and no loss of power... felt that miss at idle....
I never set a DTC but had a huge driveability issue... once the motor got nice and warmed up, it would want to stall at low throttle / low speed...
anyways... I finally found it by popping the hood and looking around with a hot running motor, not cool or off.... The vac line from the MAP sensor to the intake manifold was crushing itself under vacuum... but the line would only collapse when it got hot enough... shut the motor off and it would pop right back to shape.. making it next to impossible to find otherwise
Took about 5min and some $2 washer fluid line (i dont advise that or anything, its just what i had.. lol) and problem solved... fuel trims back to 0% (give or take 5% as it should be) and the load on the motor dropped in half... now she runs like a champ and i've used half a tank in 3 weeks.. LOL
the jist of it was... Map sensor wasnt seeing the vacuum, so it assumes im on the throttle.... richens up the mix and retards the timing... speed density systems suck.. lol.. sensors confuse themselves... one tries to lean you out, the other wants to go rich... while the ECU tries to make sense of it all... in hindsight, it all made sense... But did take a couple months of searching, especially the fuel delivery system..
Best of luck!
paul bateman wrote:figure i'll throw out my recent experience with the MAP sensor... same motor so why not..
My STFT showed -18% when idling so i was running rich but the ecu was leaning it out .... also read a 26% load on the motor at idle, numbers started to even out a bit as i started driving... Same symptoms for the most part, 16mpg and no loss of power... felt that miss at idle....
I never set a DTC but had a huge driveability issue... once the motor got nice and warmed up, it would want to stall at low throttle / low speed...
anyways... I finally found it by popping the hood and looking around with a hot running motor, not cool or off.... The vac line from the MAP sensor to the intake manifold was crushing itself under vacuum... but the line would only collapse when it got hot enough... shut the motor off and it would pop right back to shape.. making it next to impossible to find otherwise
Took about 5min and some $2 washer fluid line (i dont advise that or anything, its just what i had.. lol) and problem solved... fuel trims back to 0% (give or take 5% as it should be) and the load on the motor dropped in half... now she runs like a champ and i've used half a tank in 3 weeks.. LOL
the jist of it was... Map sensor wasnt seeing the vacuum, so it assumes im on the throttle.... richens up the mix and retards the timing... speed density systems suck.. lol.. sensors confuse themselves... one tries to lean you out, the other wants to go rich... while the ECU tries to make sense of it all... in hindsight, it all made sense... But did take a couple months of searching, especially the fuel delivery system..
Best of luck!
Excellent write up, but....... please tell all of us that you should NEVER use washer hose for vacuum. As You know, washer hose is for Pressure but will collapse under continued vacuum. I know you know that but others may not. A completely different product.
Dave
It is not uncommon for the vac hose on the Map sensor to crack over time and jack up the fueling at idle.
FU Tuning
paul bateman wrote:(i dont advise that or anything, its just what i had.. lol)
But Its done the job for a month so far... there is very little vacuum (if any) other then at idle... even my fall-apart-in-your-hands old line would hold up until i got off the gas... plus only when hot..
But I havent been able to find true vacuum lines as of yet... I hit part source, canadian tire etc... they all point to rubber fuel or coolant lines... i sigh and walk out..
Might have to drive out to napa or even the dealership... how much could they possible over-inflate vacuum lines!? lol.. But like i said... its not recommended, but in a pinch.....it works..
But im also able to change out the line on the side of the road if need be... Otherwise i'd be in much more of a hurry on this..
even now that i start searching around.. i'd like some more knowledgeable help.. sorry to kinda hijack the thread but it may be relevant to the OP as well..
Shopping for vac line... most spools i find are sold as "vacuum / washer fluid hose"
I used it because i had a few feet of it leftover after a repair... and the walls looked stiff enough... but whats the deal here? one and the same product?
I figure pressure and vacuum are essentially the same force, just opposite directions so hose properties would be similar to both and its not like this line is seeing massive forces.. like i said, this hose im using has been working perfectly thus far, should i even bother replacing it until it cracks like the old one?
Well I pulled every hose off and replaced it. Found a very small leak around my AIT sensor that I sealed. Pulled off the supercharger and repalaced all the seals as well. Even put a new O2 sensor just to try it. Still no good. Map sensor is reading just fine.
But I did find a problem. I noticed oil was bubbling out my pcv breather filter while running, so I took off the oil fill cap and sure enough I'm pumping a good flow of air out of my bottom end. Must have a couple piston rings shot. Would this be throwing a lean code, or do I still have to trace that issue down?
Heavy ass N-body
I think I narrowed it down to the pos1 O2 sensor. I had installed a heated sensor to solve the following issues codes:
P0130 - Circuit Closed Loop (CL) Performance Sensor 1
P0133 - Slow Response Sensor 1
I ran the heated 02 for almost 5k miles with no issues till now when it threw the lean codes. I unhooked the heater lines to the sensor and the car is running perfect again, but the O2 codes are back now. If plug the heater wires back in I throw lean codes in a matter of minutes. I had it at a shop for a couple days and none of the techs had any luck figuring it out. Bah.
Heavy ass N-body
